1. Field of the Invention
The present invention relates to a workpiece unloading apparatus for unloading, at least one by one, articles such as metal sheets and panels stacked and loaded, for example, on a pallet, a rack, and the like.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 3-92227 discloses an unloading apparatus equipped with special means for workpiece cutting and unloading, wherein a plurality of metal sheets and panel subjected to pressing and bending are unloaded one by one with an automatic machine from a state in which they are stacked and loaded vertically or horizontally. For example, in the automobile production process, press-formed body panels usually can be easily delivered upon stacking horizontally (stacking from bottom to top) or vertically (stacking in the horizontal direction) on a pallet or rack. Accordingly, there is a strong demand that the operation of unloading of the loaded workpieces one by one with a multipurpose commercial robot and supplying them to the next production process be automated.
Because the sheet-like workpieces thus located on a pallet or rack typically have a shape with peaks and valleys, inclination (orientation) of individual workpieces varies in the upper and lower portions of stacked pile. Furthermore, a troublesome effect is encountered in case of unloading from a state in which a plurality of articles are suspended and supported on a rack. Thus, because the workpieces are engaged with each other, when the front workpiece is unloaded, the next workpiece is also pulled out and the position and orientation change with each unloaded workpiece.
With the conventional robots of a teaching-playback system, smooth unloading operation is difficult to conduct under the above-described conditions. For this reason, the following methods have been employed: (1) a method of manually unloading the workpieces one by one, setting the workpieces in advance in a special positioning jig and then handling them with a robot; (2) a method of unloading by installing a contact-type sensor on the distal end of a robot and determining the position and orientation of workpieces by contact with a plurality of zones on the workpiece.
With the method (1), a significant manual labor is obviously required to align the workpieces. The problem associated with the method (2) is that measurements are time consuming. Moreover, the accuracy is poor and insufficient for unloading. Such problems are often encountered not only in the above-described automobile production process, but also in cases of unloading horizontally or vertically stacked metal sheets subjected to pressing or bending, flat or curved glass sheets, printed boards, flat boxes, flatly folded cloths and clothing, food plates, plastic moldings, wood materials, and the like.
It is an object of the present invention to provide a workpiece unloading apparatus constructed so as to unload the workpieces that are stacked horizontally or vertically, as described above, in an orderly manner and smoothly without manually aligning them in advance.
In accordance with the present invention, in order to resolve the above-described problems, the position and orientation of the topmost (in case of horizontal stacking) or frontmost (in case of vertical stacking) workpiece of the loaded workpieces are found with a visual sensor, and workpiece unloading means such as a robot is operated and the workpieces are unloaded based on the found position and orientation. The workpiece unloading apparatus in accordance with the present invention is mainly applicable to a case when horizontal or vertical stacking of a plurality of workpieces causes significant changes in the position or orientation of each workpiece or groups of workpieces that are to be unloaded.
Yet another problem is that unless a visual sensor is placed in an appropriate position with respect to a workpiece, which is the object of measurement, the sensor fails to detect the workpiece or the necessary measurement accuracy cannot be obtained. Therefore, when the position and orientation of the workpiece which is to be unloaded next vary significantly for each workpiece unloading operation, the workpiece measurement has to be conducted by constantly arranging the visual sensor in the appropriate position.
In accordance with the present invention, the position and orientation of the visual sensor can be varied by mounting the visual sensor on sensor movement means such as a robot. Further, the position and orientation appropriate for measuring the topmost or frontmost workpiece are determined by means for determining the workpiece measurement position of the visual sensor according to the workpieces stacking state, and the visual sensor is moved into this position. The position and orientation of the workpiece are then measured with the visual sensor, the workpiece unloading means is moved to the workpiece unloading position based on the measurement results, and the workpiece is gripped and unloaded.
In accordance with the present invention, the above-described problems are resolved by providing the following features to a workpiece unloading apparatus that unloads a plurality of workpieces stacked horizontally or vertically, at least one by one in a regular order, starting from the topmost or frontmost workpiece.
The workpiece unloading apparatus in accordance with the present invention comprises a visual sensor for finding the position and/or orientation of a workpiece, sensor measurement position determination means for determining the position of the visual sensor for measuring the topmost or frontmost workpiece, sensor movement means for moving the visual sensor to the position determined by sensor measurement position determination means, and workpiece unloading means for unloading the workpieces. Once the visual sensor has been moved by sensor movement means to the position determined by sensor measurement position determination means, the information relating to the position and/or orientation of the topmost or frontmost workpiece is obtained by the visual sensor, and workpiece unloading means unloads a workpiece based on the obtained information.
In particular, with the workpieces having a plate-like shape, when a plurality of stacked workpieces are unloaded in a regular order one by one or in groups, the position and orientation of the workpiece which is to be unloaded next change every time. However, in accordance with the present invention, because the visual sensor can be moved to a position appropriate for measurements, the workpieces can be unloaded accurately based on the measurement results obtained from the visual sensor. The workpiece unloading is conducted especially accurately when the workpiece location region is larger than the measurement field of view of the sensor.
The above-described workpiece unloading apparatus can have the following embodiments.
Examples of workpieces that can be unloaded with the workpiece unloading apparatus include metal sheets subjected to pressing or bending, flat or curved glass sheets, printed boards, flat boxes, flatly folded cloths or clothing, food plates, plastic moldings, and wood materials.
Determination of the position of visual sensor by the sensor measurement position determination means is conducted repeatedly for each unloading process of each workpiece unloading operation, periodically or non-periodically. Though the position and orientation of the workpiece which is to be unloaded next change with each unloaded workpiece, the position and orientation of the visual sensor are changed appropriately in necessary periods. As a consequence, information relating to the position and orientation of the workpieces can be obtained reliably with the visual sensor and, therefore, the workpiece unloading can be conducted accurately.
Determination of the visual sensor position with sensor measurement position determination means is conducted based on the position and/or orientation of the workpiece measured with the visual sensor during the preceding or even earlier workpiece unloading.
Determination of the visual sensor position with sensor measurement position determination means is conducted based on the visual sensor position and orientation during the preceding or even earlier workpiece unloading.
Determination of the visual sensor position with sensor measurement position determination means is conducted based on the position and/or orientation of the workpiece gripped by workpiece unloading means during the preceding or even earlier workpiece unloading.
Determination of the visual sensor position with sensor measurement position determination means is conducted based on the thickness of one workpiece which is to be unloaded, the number of workpieces, or the thickness of loaded workpieces.
Determination of the visual sensor position with sensor measurement position determination means is conducted based on information relating to the approximate position and/or orientation of the topmost or frontmost workpiece, this information being obtained with a second visual sensor in the position that was stored in advance. As a result, because two visual sensors are used for workpiece measurement, a respective time is required for processing the information obtained by the sensors. However, when the position and orientation of the workpiece which is to be unloaded next changes significantly with each unloaded workpiece, this method is effective because the workpiece measurement position of the visual sensors can be determined with good efficiency.
A three-dimensional visual sensor is used as the visual sensor.
The visual sensor whose position is determined with sensor measurement position determination means is also used as the above-mentioned second visual sensor. As a result, providing one visual sensor with two sensor functions makes it possible to construct the entire apparatus at a low cost.
A visual sensor conducting two-dimensional image processing with a camera is used as a second visual sensor.
A robot is used as sensor movement means. The visual sensor is mounted on the hand or arm of the robot.
A robot is used as workpiece unloading means.
Sensor movement means serves also as workpiece unloading means.
A plurality of workpieces, which are stacked vertically or horizontally, are housed in or supported by a housing member such as a pallet, a trolley, a rack or a hanger for suspending the workpieces, and a box.
When the number of workpieces housed in or supported by the housing member, or the thickness of loaded workpieces is below the prescribed value, a signal is output to the outside or a message is displayed. As a result, replenishment of the workpieces can be conducted in appropriate periods of time.
A specific feature is provided on the housing member, this feature being concealed by a workpiece and undetectable when the workpiece is present. A decision as to whether the workpiece is housed in or supported by the housing member is made according to the detection or non-detection of this specific feature with a visual sensor. As a result, replenishment of the workpieces can be conducted in appropriate periods of time.
Information relating to at least one of the thickness of one workpiece, the number of workpieces, and the thickness of loaded workpieces is provided by attaching to the housing member in a mechanically recognizable form, such as a bar code, figures, numerals, or marks. Any information on the thickness of one workpiece, the number of workpieces, and the thickness of loaded workpieces is automatically obtained by reading with a reading device. As a result, operation can be continuously conducted even when the number of workpieces loaded into the housing member is not constant.
When information on the thickness of loaded workpieces is used, information on the thickness of stacked workpieces may be obtained by detecting the information on the thickness of loaded workpieces with the visual sensor, second visual sensor, or other sensor means.
pressing means is provided such that when the workpieces suspended and supported on a rack or a hanger are unloaded, the presence or absence of the forward movement of the workpiece is detected from the position and/or orientation of the workpiece obtained with the visual sensor, and if the workpiece moved forward, the pressing means presses the workpiece backward.